1. Field of the Invention
The present invention relates to a scanning format converting circuit using motion vectors, and more particularly to a scanning format converting circuit for converting video signals of the interlaced scanning form involving flickers into those of the progressive scanning form free of flickers using motion vectors included in the video signals.
2. Description of the Prior Art
As a general format converting method for converting video signals of the interlaced scanning form into those of the progressive scanning form, there have been known a line doubling method, a field interpolation method and a method using motion vectors.
The line doubling method is adapted to repeat scanning for video signals for the interlaced scanning form one time and thereby double the number of scanning lines, as shown in FIG. 1. On the other hand, the field interpolation method is adapted to produce a new scanning line for an interpolation, using the mean value of adjacent scanning lines, as shown in FIG. 2. If the line doubling method is said to be the zeroth order interpolation, the field interpolation method corresponds to the first order interpolation.
The method for converting video signals of the interlaced scanning form into those of the progressive scanning form using motion vectors is adapted to motion-compensate an even field and an odd field at the point of time t-1 by motion vectors, as shown in FIG. 3a, and thereby converting the fields into those of the progressive scanning form, as shown in FIG. 3b. Where no motion is involved between adjacent fields of video signals of the interlaced scanning form, even and odd fields are overlapped with each other (namely, interleaved) so that the video signals of the interlaced scanning form can be converted into those of the progressive scanning form. Where the video signals involve motions, however, the overlap (interleaving) between even and odd fields results in an aliasing phenomenon.
In order to avoid such an aliasing phenomenon, motion vectors involved between a current field and a previous field preceding the current field are derived by macro blocks having a certain size. Thereafter, a scanning format of the first field is converted into that of the progressive scanning form using an optional method, so that it is initialized. A field value to be interpolated for the current field is derived by shifting the previous video signal converted into the progressive scanning form by the motion vector size. For a next field, the same procedure is repeated.
In accordance with the above-mentioned conventional methods, in particular, the line doubling method, however, double-thickened horizontal lines may be produced. In a case of a slant plane, a stepped artifact may produced at a diagonal edge portion of the slant plane. In the case using motion vectors, the amount of computation for estimation of motion vectors is greatly increased, even though the most accurate scanning format converting can be achieved.